U.S. Pat. No. 6,508,317 (Eddison et al) describes a down hole apparatus that generates a pulsing action, which is transmitted to a drill bit to avoid becoming stuck in a horizontal well. The manner of generating the pulsing action is to incorporate into the down hole apparatus a pressure responsive device, which expands or retracts in response to varying flow pressure. The apparatus which will hereinafter be described generates a similar pulsing action using an alternative technology.